A parliamentary system is a system of democratic governance of a state in which the executive branch derives its democratic legitimacy from, and is held accountable to, the legislature (parliament); the executive and legislative branches are thus interconnected. In a parliamentary system, the head of state is normally a different person from the head of government. This is in contrast to a presidential system in a democracy, where the head of state often is also the head of government, and most importantly, the executive branch does not derive its democratic legitimacy from the legislature.

In 1714, Prince Elector George Ludwig of Hanover, Germany, acceded to the throne of Great Britain after his cousin Queen Anne died with no heirs of her body. As King George I he chaired the cabinet and chose ministers of the government; however, he initially spoke no English. This shifted the balance of power towards the leading minister, or first minister, who de facto chaired the cabinet. During his reign, Parliament's role in controlling government and in deciding who the king could ask to form a government gradually increased. Towards the end of his reign, actual power was held by Sir Robert Walpole, who evolved as Britain's first prime minister over the years from 1721 to 1742. Later, the Great Reform Act of 1832 broadened the franchise and was accompanied by increasing parliamentary dominance, with Parliament always deciding who was prime.

A parliamentary system may be a bicameral system with two chambers of parliament (or houses): an elected lower house, and an upper house or Senate which may be appointed or elected by a different mechanism from the lower house. Another possibility is a unicameral system with just one parliamentary chamber.

Scholars of democracy such as Arend Lijphart distinguish two types of parliamentary democracies: the Westminster and Consensus systems.[1]

The Western European parliamentary model (e.g. Spain, Germany) tends to have a more consensual debating system, and usually has semi-circular debating chambers. Consensus systems have more of a tendency to use proportional representation with open party lists than the Westminster Model legislatures. The committees of these Parliaments tend to be more important than the plenary chamber. Some West European countries' parliaments (e.g. in the Netherlands and Sweden) implement the principle of dualism as a form of separation of powers. In countries using this system, Members of Parliament have to resign their place in Parliament upon being appointed (or elected) minister. Ministers in those countries usually actively participate in parliamentary debates, but are not entitled to vote.

Implementations of the parliamentary system can also differ on the manner of how the prime minister and government are appointed and as to whether the government needs the explicit approval of the parliament, rather than just the absence of its disapproval. Some countries as India also require the prime minister to be a member of the legislature, though in other countries this only exists as a convention.

By appointment by the head of state, without reference to parliament: While in practice most prime ministers under the Westminster system (including Australia, Canada, New Zealand, India and the United Kingdom) are the leaders of the largest party in parliament, technically the appointment of the prime minister is a royal prerogative exercised by the monarch or the governor-general. No parliamentary vote takes place on who is forming a government, but since parliament can immediately defeat the government with a motion of no confidence, the head of state is limited by convention to choosing a candidate who can command the confidence of parliament and has little or no influence in the decision.

The head of state nominates a candidate for prime minister who is then submitted to parliament for approval before appointment as prime minister: Example: Spain, where the King sends a nomination to parliament for approval. Also Germany where under the German Basic Law (constitution) the Bundestag votes on a candidate nominated by the federal president. In these cases, parliament can choose another candidate who then would be appointed by the head of state.

The head of state appoints a prime minister who has a set timescale within which s/he must gain a vote of confidence: (Example: Italy, Thailand)

The head of state appoints the leader of the largest or second-largest political party in the Parliament as Prime Minister: (Example: Greece)

In Israel, parliament may vote in order to call an election or pass a vote of no confidence against the government.

Other countries only permit an election to be called in the event of a vote of no confidence against the government, a supermajority vote in favour of an early election or prolonged deadlock in parliament. These requirements can still be circumvented. For example, in Germany in 2005, Gerhard Schröder deliberately allowed his government to lose a confidence motion, in order to call an early election.

In Sweden, the government may call a snap election at will, but the newly elected Riksdag is only elected fill out the previous Riksdag's term. The last time this option was used was in 1958.

Norway is unique among parliamentary systems in that the Storting always serves the whole of its four-year term.

The Parliamentary system can be contrasted with a presidential system which operates under a stricter separation of powers, whereby the executive does not form part of, nor is appointed by, the parliamentary or legislative body. In such a system, congresses do not select or dismiss heads of governments, and governments cannot request an early dissolution as may be the case for parliaments. There also exists the semi-presidential system that draws on both presidential systems and parliamentary systems by combining a powerful president with an executive responsible to parliament, as for example the French Fifth Republic.

Parliamentarianism may also apply to local governments. An example is the city of Oslo, which has an executive council (Byråd) as a part of the parliamentary system.

One of the commonly attributed advantages to parliamentary systems is that it is faster and easier to pass legislation,[3] as the executive branch is formed by the direct or indirect support of the legislative branch and often includes members of the legislature. Thus the executive (as the majority party or coalition of parties in the legislature) has a majority of the votes, and can pass legislation at will. In a presidential system, the executive is often chosen independently from the legislature. If the executive and the majority of the legislature are from different political parties, then stalemate can occur. Thus the executive might not be able to implement its legislative proposals. An executive in any system (be it parliamentary, presidential or semi-presidential) is chiefly voted into office on the basis of his or her party's platform/manifesto, and the same is also true of the legislature.

In addition to quicker legislative action, parliamentary government has attractive features for nations that are ethnically, racially, or ideologically divided. In a presidential system, all executive power is vested in one person: the president. In a parliamentary system, with a collegial executive, power is more divided. In the 1989 LebaneseTaif Agreement, in order to give Muslims greater political power, Lebanon moved from a semi-presidential system with a strong president to a system more structurally similar to classical parliamentary government. Iraq similarly disdained a presidential system out of fears that such a system would be tantamount to Shiite domination; Afghanistan's minorities refused to go along with a presidency as strong as the Pashtuns desired.[citation needed]

It can also be argued that power is more evenly spread out in parliamentary government.[citation needed] The prime minister is seldom as important as a ruling president, and there tends to be a higher focus on voting for a party and its political ideas than voting for an actual person.[citation needed]

In his 1867 book The English Constitution, Walter Bagehot praised parliamentary government for producing serious debates, for allowing change in power without an election, and for allowing elections at any time. Bagehot considered the four-year election rule of the United States to be unnatural.

A recent World Bank study found that parliamentary systems are associated with less corruption.[4]

Some constituencies may have a popular local candidate under an unpopular leader (or the reverse), forcing a difficult choice on the electorate. Mixed-member proportional representation (where voters cast two ballots) can make this choice easier by allowing voters to cast one vote for the local candidate but also cast a second vote for another party.

Although Bagehot praised parliamentary government for allowing an election to take place at any time, the lack of a definite election calendar can be abused. Previously under some systems, such as the British, a ruling party could schedule elections when it felt that it was likely to retain power, and so avoid elections at times of unpopularity. (Election timing in the UK, however, is now partly fixed under the Fixed-term Parliaments Act 2011.) Thus, by wise timing of elections, in a parliamentary system a party can extend its rule for longer than is feasible in a functioning presidential system. This problem can be alleviated somewhat by setting fixed dates for parliamentary elections, as is the case in several of Australia's state parliaments. In other systems, such as the Dutch and the Belgian, the ruling party or coalition has some flexibility in determining the election date. Conversely, flexibility in the timing of parliamentary elections can avoid periods of legislative gridlock that can occur in a fixed period presidential system.

Critics of the Westminster parliamentary system point out that people with significant popular support in the community are prevented from becoming prime minister if they cannot get elected to parliament since there is no option to "run for prime minister" as one can run for president under a presidential system. Additionally, prime ministers may lose their positions if they lose their seats in parliament, even though they may still be popular nationally. Supporters of parliamentary government respond by saying that as members of parliament, prime ministers are elected first to represent their electoral constituents and if they lose their support then consequently they are no longer entitled to be prime minister.[citation needed]

The Monarch appoints, based on recommendations from the leaders of the parties in Folketinget, the cabinet leader who is most likely to successfully assemble a Cabinet which will not be disapproved by a majority in Folketinget.